I have two AMD Radeon HD 7870s by Asus. The first is the DC2TG and the second is the DC2. I am having issues with crossfire not working well. My frame rates are not better on games such as battlefield 3 and TES V as well as others versus just the one card. I also often have hard system lockups, at least a few times per day. 

I have checked to see how both cards work individually and in both pci-e slots and they both work perfect in both slots. I have also used both crossfire bridges with no change in performance. I do have the 12.8 drivers as well as the 12.7 cap 3 profiles installed. I would appreciate any help, thanks.

OS: Windows 7 Home Premium 64 Bit

Motherboard: Asus Sabertooth 990FX

CPU: AMD FX 4170

RAM: G Skill Sniper 16 GB @ 1866

Video Card: 2 x Amd Radeon HD 7870

SSD: Samsung 64 GB

HDD: Seagate 1 TB

PSU: Cooler Master GX 750W 80 Plus Silver Certified

I'm having the same issue, only game I have that I know supports Crossfire is Max Payne 3 , tried it in this and my fps is worse than using a single card.

I also run 2x 7870's (Sapphire) I only just got the 2nd card.  Running the latest Catalyst drivers also.

Intel i5-2500k @ 4.4ghz / Asrock Z68 Extreme 4 Gen3 mb / Corsair Dominator 9-9-9-24 @ 1632mhz C9DHX 10gb / Corsair HW750 psu / CoolerMaster HAF-X Case / Samsung 1TB F1 Spinpoint SATA2 x 2 / Seagate Barracude 1TB SATA3 / Sandisk Extreme 240gb SSD / Sapphire HD7870 OC edition x2 CrossFire